A variety of bioacoustic sensors have been developed to detect sounds produced by the body, such as heart and lung sounds. Known devices range from mechanical devices, such as stethoscopes, to various electronic devices, which can typically include microphones and transducers.
Although many electronic bioacoustic sensors are available on the market, they have yet to gain universal acceptance by the physicians and other medical practitioners. Possible reasons for non-acceptance of electronic bioacoustic sensors include the production of noise or artifacts that disturb the clinician during patient evaluation, as well as limitations associated with amplification and reproduction of certain biological sounds of interest. In general, bioacoustic sensors, including electronic stethoscopes, are preferentially designed to detect acoustic vibrations emanating from the body. In practice, however the acoustic vibrations detected include both bodily acoustic sounds indicative of physiological parameters (e.g., breathing sounds indicative of respiratory rate, heart sounds, etc.) and acoustic vibrations from environmental noise (sometimes referred to as ambient noise) emanating from one or more noise sources. For example, the acoustic noise may include noise from an external noise source, such as electronics (e.g., computers, medical equipment, motors, pumps, fans, alarms, or other electronics, etc.), noise from other people such as visiting family members and medical personnel in the vicinity of the patient, vehicle noise (e.g., in a helicopter), etc. In some circumstances, the acoustic noise includes sounds coming from the patient that are not indicative of measured physiological parameters. Such sounds may include patient speech, coughing, etc. As a result, the bioacoustic sensor, typically a transducer, will produce a signal indicative of all detected acoustic vibrations. Each signal will therefore include a physiological sound component representative of the physiological parameter of interest and an acoustic noise component representative of environmental and/or other noise.
The signal-to-noise ratio of bioacoustic sensor signals is generally reduced due to the presence of the acoustic noise, regardless of the source. In some circumstances, a reduced signal-to-noise ratio can make it difficult to distinguish the physiological sound components of the signal from the noise components to provide accurate measurements. This problem is particularly exacerbated in some emergency environments, such as in-flight helicopters and ambulances, where the noise detected by the sensor can be orders of magnitude greater than the body sounds of interest.
Various techniques are known in the art to reduce the presence and effect of noise in the acoustic signal. In a typical approach, as exemplified by US Publication No. 2011/1213271 (Telfort et al.), systems are designed to collect signals from more than one acoustic sensing element, and then combine (e.g., summing, subtracting, averaging, etc.) the respective outputs from those sensing elements in a manner that tends to reinforce the physiological components of the signals while tending to cancel or reduce the noise components of the signals.